1. Field of the Invention
This invention relates to room temperature vulcanizing (RTV) silicone compositions, curable in the presence of moisture, comprising polydiorganosiloxanes, acyloxy-functional crosslinkers and additives such as metal acetates and metal acetylacetonates which provide oil resistance to the cured composition.
2. Background Information
The use of room temperature vulcanizing (RTV) silicone sealants for creating formed-in-place gaskets is well known in both original equipment manufacture and in repair and maintenance. A problem with certain conventional silicone sealants is their tendency in the presence of hot oil to lose structural integrity leading to seal failure. Therefore, it is desirable to have silicone sealants providing increased oil resistance as demonstrated by increased tensile strength in the presence of hot oil.
Getson, et al., U.S. Pat. No. 4,123,472, describe oil resistant organopolysiloxane compositions prepared by polymerizing an acrylic ester and an acrylic nitrile in the presence of an organopolysiloxane and a free radical initiator at an elevated temperature. This modified polysiloxane when mixed with a crosslinking agent, such as an acyloxy-functional silane, and exposed to moisture and heat aging, cures to an oil resistant composition.
Beers, U.S. Pat. No. 4,680,363, describes a process for forming a one component RTV silicone rubber composition with good bonding properties at high humidity conditions, and Beers, U.S. Pat. No. 4,758,611, describes the RTV silicone composition comprising a silanol-endblocked diorganopolysiloxane, an acyloxy-functional crosslinking agent, a curing promoter which is a salt of a carboxylic acid, and a magnesium or zinc salt of a carboxylic acid as an acid scavenger.
Beers, U.S. Pat. No 4,833,037, describes a laminated article comprising a plurality of metal substrates, wherein between the metal substrates there is a layer of a one component RTV silicone rubber composition with good bonding properties at high humidity conditions, comprising a silanol-endblocked diorganopolysiloxane, an acyloxy-functional crosslinking agent, a curing promoter which is a salt of a carboxylic acid, and an acid scavenger selected from magnesium or zinc oxide, magnesium, aluminum or zinc metal, magnesium or zinc salt of a carboxylic acid, or mixtures thereof.
Beers, U.S. Pat. No. 4,257,932 describes a self-bonding silicone RTV comprising a silanol endstopped polydiorganosiloxane; a fluid polysiloxane having a high degree of tri or tetrafunctionality; a silica filler; a crosslinking silane evolving relatively low volatility carboxylic acid fragments on hydrolysis; and a tin catalyst. Beers, also discloses the improvement of high temperature performance with the addition of an iron oxide thermal stabilizer.
Letoffe, et al., U.S. Pat. No. 4,797,462, describe organopolysiloxanes curable into elastomeric state and well adapted as sealing materials for a variety of substrates, comprising a polyhydroxylated polysiloxane, a polyacyloxysilane crosslinking agent and an effective amount of at least one of calcium oxide, strontium oxide and/or barium oxide cure accelerator therefor.
The present inventors have unexpectedly determined that the addition of a metal acetate, preferably along with a metal acetylacetonate, to a RTV silicone composition comprising a polydiorganosiloxane, acyloxy-functional crosslinker, filler, and tin catalyst results in a cured composition having increased hot oil resistance. In addition, these compositions may find use when cured as sealants, adhesives, gaskets, coatings, molding and potting compounds, and gels.
The objective of this invention is to provide a RTV silicone composition having increased hot oil resistance upon curing.